Magneto-resistive effect device, magnetic head gimbal assembly, magnetic recording/reproduction device, strain sensor, pressure sensor, blood pressure sensor, and structural health monitoring sensor

ABSTRACT

According to one embodiment, a magneto-resistive effect device, includes a stacked body stacked on a substrate, a pair of first electrodes that feeds current to the stacked body, a strain introduction member, and a second electrode for applying a voltage to the strain introduction member. The stacked body includes a first magnetic layer that includes one or more metals selected from the group consisting of iron, cobalt, and nickel, a second magnetic layer stacked on the first magnetic layer, having a composition that is different from the first magnetic layer, and a spacer layer disposed between the first magnetic layer and the second magnetic layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 13/246,069 filed Sep. 27, 2011,and claims the benefit of priority under 35 U.S.C. §119 from JapanesePatent Application No. 2011-066017 filed Mar. 24, 2011; the entirecontents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magneto-resistiveeffect device, a magnetic head gimbal assembly, a magneticrecording/reproduction device, a strain sensor, a pressure sensor, ablood pressure sensor, and a structural health monitoring sensor.

BACKGROUND

The performance of magnetic devices using a stacked structure ofmagnetic material layers, in particular the performance of magneticheads, has dramatically improved. In particular, in the technical fieldof magnetic heads using spin-valve films (Spin-Valve: SV film) there hasbeen great progress.

A “spin-valve film” is a stacked film in which a nonmagnetic layer issandwiched between two ferromagnetic layers, and one ferromagnetic layer(referred to as a “pinned layer”) is a layer whose magnetizationdirection is pinned by an antiferromagnetic layer, and the otherferromagnetic layer is a layer whose magnetization can respond toexternal magnetic fields (referred to as a “free layer”).

The spin-valve film functions as a type of variable resistance device.The resistance of carriers that move through the spin-valve film dependson the carrier spin state. Therefore, by changing the spin state of thespin-valve film with an external magnetic field, it is possible tochange the resistance state of the spin-valve film.

The magneto-resistance effect (the MR effect) in which electricalresistance is varied by an external magnetic field gives rise to manyphysical phenomena. The most well-known are giant magnetoresistance(GMR) and tunneling magnetoresistance (TMR).

The electrical resistance state of a magneto-resistive effect devicethat includes a spin-valve film is determined by adjacent ferromagneticlayers, for example by the relative relationship between magnetizationdirections of the pinned layer and the free layer. Typically, in aspin-valve film, when the magnetization directions of the twoferromagnetic layers are aligned parallel, the electrical resistancestate is in the “low resistance state”. This state is conventionallyrepresented as the “0” state. On the other hand, when the magnetizationdirections of the two ferromagnetic layers are aligned antiparallel, theelectrical resistance state is in the “high resistance state”. Thisstate is conventionally represented as the “1” state. When the anglebetween the magnetization directions of the adjacent layers is anintermediate angle, the resistance state is intermediate. Amagneto-resistive effect device that uses this phenomenon is widely usedin reading heads for HDDs.

A magneto-resistive effect device with two free layers and that does nothave a pinned layer and a pinning layer is being investigated as a headsuitable for narrow gaps that are suitable for high densification, incontrast to magneto-resistive effect devices having a conventionalpinned layer. In this structure, top and bottom magnetic layers with aspacer layer disposed therebetween both function as free layers.However, when the two free layers are oriented in the same magnetizationdirection, they do not function as a magnetic field sensor, so it isnecessary that there be some measure to bias the two magnetic layers indifferent directions. This cannot be achieved with a bias using just aconventional hard bias layer, but an extremely complex bias isnecessary. Therefore, at present the magneto-resistive effect devicewith two free layers has not reached the stage of practical use.

On the other hand, strain sensors that use the MR effect have beenproposed, and a strain sensor using the MR effect has an area smallerthan a conventional strain sensor, and can achieve extremely highsensitivity.

However, in a strain sensor that includes a conventional pinned layer, aspacer layer, and a free layer, there is only one free layer whichoperates magnetically as a unit (if a free layer is formed in a stackedfilm, and if there is rotation of magnetization as a unit magnetically,it becomes a single free layer). In this case, if the free layer usesthe inverse magnetostrictive effect to detect strain, themagnetostriction coefficient of the free layer is either positive ornegative only, so meaningful magnetization rotation only occurs for oneof compressive stresses or tensile stresses, so the strain sensor isonly capable of detecting one type of strain state. In this case thereis the problem that when it is necessary to detect the strain at manypoints, the total sensitivity is reduced. A strain sensor that iscapable of detecting either compressive stresses or tensile stresses isnecessary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a magneto-resistive effectdevice according to a first embodiment;

FIGS. 2A through 2C illustrate changes in magnetization direction when astrain is applied to the magnetic layers having positive and negativemagnetostriction coefficients in the magneto-resistive effect deviceaccording to the first embodiment, FIG. 2A illustrates a tensile strain,FIG. 2B illustrates a compressive strain, and FIG. 2C is across-sectional view of the plane A-A′ indicated in FIG. 2A;

FIG. 3 is a perspective view illustrating a magnetic head according to asecond embodiment;

FIGS. 4A through 4C illustrate magnetization directions of themagneto-resistive effect device, FIG. 4A illustrates a case where thereis no external magnetic field, FIG. 4B illustrates a case where anexternal magnetic field is directed away from the device, and FIG. 4Cillustrates a case where an external magnetic field is directed towardsthe device;

FIGS. 5A through 5C illustrate the magnetization directions of themagneto-resistive effect device, FIG. 5A illustrates a case where thereis no external magnetic field, FIG. 5B illustrates a case where anexternal magnetic field is directed away from the device, and FIG. 5Cillustrates a case where an external magnetic field is directed towardsthe device;

FIG. 6 is a perspective view illustrating a magnetic head according to athird embodiment;

FIGS. 7A and 7B are perspective views illustrating a magnetic headaccording to a fourth embodiment, and FIG. 7C is a cross-sectional viewat the plane A-A′ indicated on FIG. 7B;

FIG. 8 is a perspective view illustrating a magnetic head according to afifth embodiment;

FIG. 9 is a perspective view illustrating a magnetic head according to asixth embodiment;

FIG. 10 is a perspective view illustrating a magnetic head according toa seventh embodiment;

FIG. 11 is a perspective view illustrating a magnetic head according toan eighth embodiment;

FIG. 12 is a perspective view illustrating a magnetic head according toa ninth embodiment;

FIGS. 13A and 13B are perspective views illustrating a magnetic headgimbal assembly according to a tenth embodiment;

FIG. 14 is a perspective view illustrating a magneticrecording/reproduction device according to an eleventh embodiment;

FIG. 15 is a cross-sectional view illustrating a strain sensor accordingto a twelfth embodiment;

FIG. 16 is a cross-sectional view illustrating the operation of thestrain sensor according to the twelfth embodiment;

FIG. 17 is a cross-sectional view illustrating the operation of thestrain sensor according to the twelfth embodiment;

FIGS. 18A and 18B illustrate the operation of the strain sensoraccording to the twelfth embodiment, FIG. 18A illustrates a case inwhich a tensile strain is applied, and FIG. 18B illustrates a case inwhich a compressive strain is applied;

FIGS. 19A, 19B, and 19C illustrate the operation of the strain sensoraccording to the twelfth embodiment, FIG. 19A illustrates a case inwhich a tensile strain is applied in an arbitrary direction, FIG. 19Billustrates a case in which a compressive strain is applied in anarbitrary direction, and FIG. 19C illustrates a case in which acompressive strain is applied and prior to application of the strain themagnetization directions of the two ferromagnetic layers areantiparallel;

FIG. 20 is a cross-sectional view illustrating a variation of the strainsensor according to the twelfth embodiment;

FIG. 21 is a cross-sectional view illustrating a strain sensor accordingto a thirteenth embodiment;

FIGS. 22A through 22D illustrate the operation of the strain sensor inaccordance with the thirteenth embodiment, FIG. 22A illustrates a casewhere a compressive strain is applied to the device A, FIG. 22Billustrates a case where a tensile strain is applied to the device A,FIG. 22C illustrates a case where a compressive strain is applied to thedevice B, and FIG. 22D illustrates a case where a tensile strain isapplied to the device B;

FIG. 23 is a perspective view illustrating a strain sensor according toa fourteenth embodiment;

FIG. 24 illustrates a magneto-resistive effect device in the strainsensor according to the fourteenth embodiment;

FIG. 25 is a perspective view illustrating a magneto-resistive effectdevice according to a fifteenth embodiment;

FIGS. 26A and 26B illustrate the stacked body of the magneto-resistiveeffect device according to the fifteenth embodiment, FIG. 26Aillustrates a case of application of a tensile strain, and FIG. 26Billustrates a case of application of a compressive strain;

FIG. 27 is a cross-sectional view illustrating a blood pressure sensoraccording to a sixteenth embodiment;

FIG. 28 illustrates the blood pressure sensor according to the sixteenthembodiment;

FIG. 29 illustrates a blood pressure measuring system according to aseventeenth embodiment;

FIG. 30 is a flowchart showing the operation of the blood pressuremeasurement system according to the seventeenth embodiment;

FIG. 31 illustrates a structural health monitoring sensor according to anineteenth embodiment; and

FIG. 32 illustrates the structural health monitoring sensor according tothe nineteenth embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a magneto-resistive effectdevice, includes a stacked body stacked on a substrate, a pair of firstelectrodes that feeds current to the stacked body, a strain introductionmember, and a second electrode for applying a voltage to the strainintroduction member. The stacked body includes a first magnetic layerthat includes one or more metals selected from the group consisting ofiron, cobalt, and nickel, a second magnetic layer stacked on the firstmagnetic layer, having a composition that is different from the firstmagnetic layer, and a spacer layer disposed between the first magneticlayer and the second magnetic layer. The strain introduction memberapplies strain to the stacked body. The strain introduction member isprovided near the stacked body. By applying strain to the stacked body,the strain introduction member biases magnetization directions of thefirst magnetic layer and the second magnetic layer in differentdirections. The magnetization directions of the first magnetic layer andthe second magnetic layer are changed by the application of an externalmagnetic field. The external magnetic field is detected by a change inresistance between the first electrodes due to the change in themagnetization directions.

According to another embodiment, a magnetic head gimbal assemblyincludes a magneto-resistive effect device. a magneto-resistive effectdevice, includes a stacked body stacked on a substrate, a pair of firstelectrodes that feeds current to the stacked body, a strain introductionmember, and a second electrode for applying a voltage to the strainintroduction member. The stacked body includes a first magnetic layerthat includes one or more metals selected from the group consisting ofiron, cobalt, and nickel, a second magnetic layer stacked on the firstmagnetic layer, having a composition that is different from the firstmagnetic layer, and a spacer layer disposed between the first magneticlayer and the second magnetic layer. The strain introduction memberapplies strain to the stacked body. The strain introduction member isprovided near the stacked body. By applying strain to the stacked body,the strain introduction member biases magnetization directions of thefirst magnetic layer and the second magnetic layer in differentdirections. The magnetization directions of the first magnetic layer andthe second magnetic layer are changed by the application of an externalmagnetic field. The external magnetic field is detected by a change inresistance between the first electrodes due to the change in themagnetization directions.

According to another embodiment, a magnetic recording/reproductiondevice includes a magnetic head gimbal assembly that includes amagneto-resistive effect device, a magnetic head that includes themagneto-resistive effect device, mounted on the magnetic head gimbalassembly, and a magnetic recording medium that reproduces informationusing the magnetic head. The magneto-resistive effect device includes astacked body stacked on a substrate, a pair of first electrodes thatfeeds current to the stacked body, a strain introduction member, and asecond electrode for applying a voltage to the strain introductionmember. The stacked body includes a first magnetic layer that includesone or more metals selected from the group consisting of iron, cobalt,and nickel, a second magnetic layer stacked on the first magnetic layer,having a composition that is different from the first magnetic layer,and a spacer layer disposed between the first magnetic layer and thesecond magnetic layer. The strain introduction member applies strain tothe stacked body. The strain introduction member is provided near thestacked body. By applying strain to the stacked body, the strainintroduction member biases magnetization directions of the firstmagnetic layer and the second magnetic layer in different directions.The magnetization directions of the first magnetic layer and the secondmagnetic layer are changed by the application of an external magneticfield. The external magnetic field is detected by a change in resistancebetween the first electrodes due to the change in the magnetizationdirections.

According to another embodiment, a strain sensor includes a substrate, astacked body fixed to the substrate, and a pair of electrodes that feedscurrent to the stacked body. The stacked body includes a first magneticlayer that includes one or more metals selected from the groupconsisting of iron, cobalt, and nickel, a second magnetic layer stackedon the first magnetic layer, having a composition that is different fromthe first magnetic layer, and a spacer layer disposed between the firstmagnetic layer and the second magnetic layer. The magnetization of boththe first magnetic layer and the second magnetic layer rotates due toexternal strain applied to the stacked body. The external strain isdetected by a change in the resistance between the electrodes associatedwith the rotation of the magnetization of the first magnetic layer andthe second magnetic layer.

According to another embodiment, a pressure sensor includes a strainsensor. The strain sensor includes a substrate, the stacked body fixedto the substrate, and a pair of electrodes that feeds current to thestacked body. The substrate includes a flexible membrane to which astacked body is fixed and a support part that supports the membrane. Thestacked body includes a first magnetic layer that includes one or moremetals selected from the group consisting of iron, cobalt, and nickel, asecond magnetic layer stacked on the first magnetic layer, having acomposition that is different from the first magnetic layer, and aspacer layer disposed between the first magnetic layer and the secondmagnetic layer. The magnetization of both the first magnetic layer andthe second magnetic layer rotates due to external strain applied to thestacked body. The external strain is detected by a change in theresistance between the electrodes associated with the rotation of themagnetization of the first magnetic layer and the second magnetic layer.External pressure is detected by detecting strain on the membrane due toexternal pressure.

According to another embodiment, a blood pressure sensor that monitorsthe blood pressure of a person or an animal includes a strain sensor.The strain sensor includes a substrate, a stacked body fixed to thesubstrate, and a pair of electrodes that feeds current to the stackedbody. The stacked body includes a first magnetic layer that includes oneor more metals selected from the group consisting of iron, cobalt, andnickel, a second magnetic layer stacked on the first magnetic layer,having a composition that is different from the first magnetic layer,and a spacer layer disposed between the first magnetic layer and thesecond magnetic layer. The magnetization of both the first magneticlayer and the second magnetic layer rotates due to external strainapplied to the stacked body. External strain is detected by a change inthe resistance between the electrodes associated with the rotation ofthe magnetization of the first magnetic layer and the second magneticlayer.

According to another embodiment, a structural health monitoring sensorthat performs structural condition monitoring to monitor a strain stateof a bridge or building structure include a strain sensor. The strainsensor includes a substrate, a stacked body fixed to the substrate, thestacked body, and a pair of electrodes that pass current through thestacked body. The stacked body includes a first magnetic layer thatincludes one or more metals selected from the group consisting of iron,cobalt, and nickel, a second magnetic layer stacked on the firstmagnetic layer, having a composition that is different from the firstmagnetic layer, and a spacer layer disposed between the first magneticlayer and the second magnetic layer. The magnetization of both the firstmagnetic layer and the second magnetic layer rotate due to externalstrain applied to the stacked body. External strain is detected by achange in the resistance between the electrodes associated with therotation of the magnetization of the first magnetic layer and the secondmagnetic layer.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

First Embodiment

Hereinafter, embodiments of the invention will be explained below withreference to the drawings.

First, a first embodiment will be described.

FIG. 1 is a perspective view illustrating the magneto-resistive effectdevice according to the first embodiment.

As illustrated in FIG. 1, a magneto-resistive effect device 10 has astacked structure that includes a ferromagnetic layer 12 whosemagnetization direction can be rotated by an external magnetic field,and a ferromagnetic layer 11 stacked on the ferromagnetic layer 12 andwhose magnetization direction can be rotated by an external magneticfield. In this embodiment, a spacer layer 13 is provided between theferromagnetic layer 11 and the ferromagnetic layer 12. The ferromagneticlayer 11 and the ferromagnetic layer 12 are made from materials thatexhibit the inverse magnetostrictive effect. However, the polarities ofthe inverse magnetostrictive effect of the ferromagnetic layer 11 andthe ferromagnetic layer 12 are mutually opposite. For example, theferromagnetic layer 11 has a positive magnetostriction coefficient, andthe ferromagnetic layer 12 has a negative magnetostriction coefficient.

In the following, the stacked body in which the ferromagnetic layer 11,the spacer layer 13, and the ferromagnetic layer 12 are stacked isreferred to as a “stacked body 19”, the direction in which theferromagnetic layer 11, the spacer layer 13, and the ferromagnetic layer12 are stacked is referred to as the “stacking layer”, and any directionnormal to the stacking direction is referred to as the “in-planedirection”.

The following are specific examples of materials with differentmagnetization polarity of the ferromagnetic layer 11 and theferromagnetic layer 12 of the magneto-resistive effect device.

The magnetic layer that has a positive magnetostriction coefficientincludes one or more metals selected from the group consisting of iron,cobalt, and nickel.

On the other hand, the magnetic layer that has a negativemagnetostriction coefficient includes basically one or more metalsselected from the group consisting of iron, cobalt, and nickel. Ofthese, the use of a material that includes one or more of the metalsselected from the group consisting of nickel and samarium iron (SmFe) issuitable. In the case of a metal spacer layer, a CoFe alloy layer issuitable as a material that has negative magnetostriction.

In the following, as an example, the stacked body 19 that includes amagnetic layer having a positive magnetostriction coefficient, a spacerlayer, and a magnetic layer having a negative magnetostrictioncoefficient is described.

Normally, the magnetostriction of a magnetic layer is determined by thecomposition of the magnetic layer. The general trends of thesecompositions have been investigated in many publications to date.However, a characteristic situation that occurs with very thin films isthat the actual magnetostriction is greatly affected by the materialadjacent to a magnetic layer.

If an oxide material is used as the spacer layer 13 (a tunnel barrierlayer such as magnesium oxide (MgO) or a CCP layer that is describedlater), when a magnetic layer that includes cobalt iron (CoFe) or thelike is used at an interface with the spacer layer 13, the magneticlayers normally have positive magnetostriction within 1 to 2 nm of thetop and bottom surfaces of spacer layer 13. This is because oxide layerssuch as CoFeBO_(x), CoO_(x), NiO_(x), and FeO_(x), and so on arematerials that have positive magnetostriction. Next, in this embodiment,a constitution that exhibits different positive and negativemagnetostriction is formed using the ferromagnetic layers 11 and 12. Theinterface of the oxide layer already exhibits positive magnetostriction,so it is comparatively easy to form a magnetic layer with positivemagnetostriction as either the whole free layer 11 or the whole freelayer 12. Therefore, at the other interface, in order to form negativemagnetostriction, by stacking a magnetic layer with large negativemagnetostriction onto the oxide interfacial layer that has positivemagnetostriction, the magnetic layer with negative magnetostriction canbe formed as the total free layer 11 or the free layer 12. Largenegative magnetostriction can be achieved using a nickel (Ni) richalloy.

Other examples for forming negative magnetostriction include, forexample, nickel (Ni), NiFe alloy (including not less than 85 at % Ni),SmFe, and so on. If magnetic material is formed from in a plurality oflayers, it forms a magnetic layer with a magnetization direction actingmagnetically as a unit. The magnetostriction of the magnetic layers isdetermined by the total stacked film constitution of the magnetic layers(on the other hand, the other magnetic layer with the nonmagnetic layerdisposed therebetween functions as a separate magnetic layer, so themagnetostriction is defined as a separate value.

A specific example of the stacked film constitution of the ferromagneticlayer 11/spacer layer 13/ferromagnetic layer 12 is a stacked film ofCo₉₀Fe₁₀/CoFeB/MgO/CoFeB/Ni₉₅Fe₅, with film thicknesses of 2 nm/1 nm/1.5nm/1 nm/2 nm respectively. Here, the Co₉₀Fe₁₀/CoFeB layers function as asingle magnetic layer that exhibits positive magnetostriction, and theCoFeB/Ni₉₅Fe₅ layers function as a single magnetic layer that exhibitsnegative magnetostriction. The MgO layer is the spacer layer.

There are various types of spacer layer depending on the physicalmechanism of the magnetoresistance.

When using the GMR effect of a current in plane (CIP) structure or acurrent perpendicular to the plane (CPP) structure, a nonmagnetic metalis used as the material of the spacer layer. Also, the nonmagnetic metalmay be one metal selected from the group consisting of copper, gold,silver, aluminum, and chromium.

Here, a CIP structure is a structure in which a pair of electrodes isprovided at two ends in the in-plane direction of the stacked body ofthe ferromagnetic layer 11 and the ferromagnetic layer 12, and the pairof electrodes feeds current to the stacked body in the in-planedirection. Also, a CPP structure is a structure in which a pair ofelectrodes is provided at the two ends in the stacking direction of thestacked body of the ferromagnetic layer 11 and the ferromagnetic layer12, and current flows through the stacked body in the stackingdirection.

The spacer layer is also used in a current configured path (CCP)structure, which does not have a uniform metal layer. The spacer layerin a CCP structure is an insulating layer with a film thickness in theorder of nanometers, with electrically conducting material embedded inthrough holes. The advantage of a spacer layer with a CCP structure isthat the MR effect is increased, while maintaining a low resistance. Thematerial of the electrically conducting material in a spacer layer witha CCP structure is one metal selected from the group consisting ofcopper, gold, silver, aluminum, and chromium. The material of theinsulating material of a spacer layer with a CCP structure is an oxideor nitride of one type of metal selected from the group consisting ofaluminum, titanium, zinc, silicon, hafnium, tantalum, molybdenum,tungsten, niobium, chromium, magnesium, and zirconium.

If TMR is used, the spacer layer 13 is formed from a typical insulatingmaterial such as magnesium oxide, in order to obtain high electricalresistance. A spacer layer made from such an insulating materialfunctions as a tunnel barrier layer. Here, tunnel barrier layer refersto an insulating layer through which current can flow as a result of thetunnel effect. Besides magnesium oxide as described above, magnesiumnitride, or an oxide or nitride of one metal selected from the groupconsisting of aluminum, titanium, zinc, silicon, hafnium, tantalum,molybdenum, tungsten, niobium, chromium, and zirconium can be used asthe material of the tunnel barrier layer.

As stated above, of the two ferromagnetic layers included in themagneto-resistive effect device, one exhibits positive magnetostrictioncoefficient, and the other exhibits negative magnetostrictioncoefficient, with the spacer layer disposed therebetween. For example,in the process of forming the films to form the stacked body 19illustrated in FIG. 1, the layer with the positive magnetostrictioncoefficient, the spacer layer, and the layer with the negativemagnetostriction coefficient may be formed in that order from the bottomup, or conversely the layer with the negative magnetostrictioncoefficient, the spacer layer, and the layer with the positivemagnetostriction coefficient may be formed in that order from the bottomup.

In order to explain the operating principle of this embodiment asillustrated in FIG. 1, first the state in which the external strain isvery small is illustrated. The initial magnetization directions 14 and15 of the ferromagnetic layer 11 and the ferromagnetic layer 12 areantiparallel. This corresponds to a state of static magnetic couplingbetween the two magnetic layers, or a case in which theantiferromagnetic coupling component due to RKKY interaction is large,or the like. However, there is also the case where the initialmagnetization directions of the first ferromagnetic layer 11 and thesecond ferromagnetic layer 12 are parallel such as when there is strongmagnetic field coupling between the two ferromagnetic layers. In thefollowing explanation, the principle is explained in substantially thesame way whether the initial state is a parallel magnetization state oran antiparallel magnetization state.

Next, operation of the magneto-resistive effect device according to thefirst embodiment will be described.

First, the magnetostrictive effect is explained.

The magnetostrictive effect is the generation of a strain in a magneticmaterial by changing the magnetization direction of the magneticmaterial. The strain generated by the magnetostrictive effect depends onthe magnitude and direction of magnetization. Therefore, the magnitudeof the strain due to the magnetostrictive effect is controlled by themagnitude and direction of magnetization. Also, the magnitude of thestrain due to the magnetostriction greatly depends on the characteristicmagnetostriction coefficient of the magnetic material. The value of theratio of the change in strain in the state where the magnetization issaturated is referred to as the magnetostriction coefficient.

There is also the inverse magnetostrictive effect, which is the oppositephenomenon of the magnetostrictive effect. The inverse magnetostrictiveeffect is the phenomenon in which the direction of magnetization of amagnetic material is changed by an externally applied strain. Themagnitude of the change in magnetization direction in the inversemagnetostrictive effect depends on the magnitude of the externallyapplied strain and the characteristic magnetostriction coefficient ofthe magnetic material. The magnetostrictive effect and the inversemagnetostrictive effect are physically symmetrical, and themagnetostriction coefficient has the same value in both effects.

The magnetostriction coefficient in the magnetostrictive effect and theinverse magnetostrictive effect can be either a positivemagnetostriction coefficient or a negative magnetostriction coefficient,depending on the magnetic material.

In the inverse magnetostrictive effect, in the case of a magneticmaterial with a positive magnetostriction coefficient, when a tensilestrain is applied to the magnetic material, the direction ofmagnetization of the magnetic material is changes to a direction thatcoincides with the direction of the applied strain. It is this directionbecause this direction is energetically stable. Also, when a compressivestrain is applied to the magnetic material, the direction ofmagnetization of the magnetic material changes to a direction that isnormal to the direction of the applied strain.

On the other hand, in the case of a magnetic material with a negativemagnetostriction coefficient, the opposite is the case. In other words,when a compressive strain is applied to the magnetic material, themagnetization direction of the magnetic material changes to a directionthat coincides with the direction of the applied strain. On the otherhand, when a tensile strain is applied, the direction of magnetizationof the magnetic material changes to a direction that is normal to thedirection of the applied strain.

In this way, in states in which strain with a single polarity is applied(in other words, only one of either compression or tension), thedirections of magnetization of the two magnetic layers having differentpolarity magnetostriction coefficients change to different directions.By using this phenomenon it is possible to realize a bias structure withtwo free layers. In other words, it is possible to set the angle betweenthe magnetization directions of the two magnetic layers to about 90degrees.

FIGS. 2A through 2C illustrate the change in magnetization directionwhen a strain is applied to the magnetic layers having positive andnegative magnetostriction coefficients in the magneto-resistive effectdevice according to the first embodiment, FIG. 2A illustrates a tensilestrain, FIG. 2B illustrates a compressive strain, and FIG. 2C is across-sectional view of the plane A-A′ indicated in FIG. 2A.

As illustrated in FIG. 2A, if a tensile strain 16 a is applied to themagneto-resistive effect device 10, the magnetization direction 14 ofthe ferromagnetic layer 11 which has a positive magnetostrictioncoefficient changes so that the angle with the direction of the tensilestrain 16 a becomes smaller, in other words, rotates towards thedirection of the tensile strain 16 a to a magnetization direction 17 a.Conversely, the magnetization direction 15 of the ferromagnetic layer 12which has a negative magnetostriction coefficient changes so that theangle with the direction of the tensile strain 16 a becomes larger, inother words, rotates towards a direction normal to the direction of thetensile strain 16 a to a magnetization direction 18 a.

On the other hand, if a compressive strain 16 b is applied instead ofthe tensile strain 16 a, the opposite occurs. In other words, asillustrated in FIG. 2B, the magnetization direction 14 of theferromagnetic layer 11 which has a positive magnetostriction coefficientrotates towards a direction normal to the direction of the compressivestrain 16 b to a magnetization direction 17 b. Conversely, themagnetization direction 15 of the ferromagnetic layer 12 which has anegative magnetostriction coefficient rotates towards the direction ofthe compressive strain 16 b to a magnetization direction 18 b.

In this way, regardless of the polarity of the strain, such as tensilestrain or compressive strain, and even if a single polarity strain isapplied, the magnetization directions of the two magnetic layers whichhave positive and negative magnetostriction coefficients are induced toapproach a right angle to each other. Therefore, the application ofstrain can be used to bias the magnetization directions of the two freelayers in different directions.

Next, the effect of the magneto-resistive effect device according to thefirst embodiment will be described.

As stated previously, in a magneto-resistive effect device that includestwo free layers, a bias structure to orient the magnetization directionsof the two magnetic layers in different directions was extremelydifficult.

However, by using materials with different magnetostriction polarity inthe two ferromagnetic layers with the spacer layer disposedtherebetween, as in this embodiment, and applying an external strainwith a single polarity to the stacked film, it is possible to achieve anappropriate bias with respect to the magnetization directions of the twomagnetic layers. In other words, it is possible to realize amagneto-resistive effect device with thin film thickness that does nothave a pinned layer and a pinning layer. In this way it is possible torealize a magneto-resistive effect device suitable for highdensification and suitable for narrow gaps.

Second Embodiment

Next a second embodiment will be described.

This embodiment is an embodiment of a magnetic head.

The magnetic head according to this embodiment is provided with themagneto-resistive effect device according to the first embodiment.

FIG. 3 is a perspective view illustrating the magnetic head according tothe second embodiment.

As illustrated in FIG. 3, a magnetic head 20 is provided with thestacked body 19 that constitutes the magneto-resistive effect device 10,and, if the stacking direction is the vertical direction, with a topelectrode 21 on the top surface thereof, and a bottom electrode 22 onthe bottom surface thereof.

As illustrated in FIG. 3, one side surface of the four side surfaces ofthe stacked body 19 is taken to be an ABS surface 23. In the ABS surface23, both the top electrode 21 and the bottom electrode 22 are exposed.In other words, an end edge of the top electrode 21 and an end edge ofthe bottom electrode 22 form part of the ABS surface 23. In thisembodiment, an example in which the magneto-resistive effect device 10is applied to a magnetic head that measures external magnetic fields,for example the magnetic field from magnetic media, is explained. TheABS surface 23 is disposed facing a rotating magnetic medium. In thisway, the magnetization directions of the two magnetic layers of thestacked body 19 are changed by the magnetic flux generated by themagnetic medium.

In this embodiment, strain can be introduced to the magneto-resistiveeffect device 10 by using stress generated during manufacture of themagnetic head 20, but the strain can also be actively introduced byvarious means.

In the process of producing a magnetic head, after forming the devicesat wafer level, a lapping process is carried out that mechanicallygrinds the film cross-section of the magneto-resistive effect device.The orientation of this lapping is applied from one cross-section, so astress with a single polarity is applied to the magneto-resistive effectdevice. This stress can be used as a source of externally appliedstrain. In other words, the strain generated by grinding from the filmcross-section of the stacked body can be used as the strain applied tothe stacked body.

Also, while manufacturing the magneto-resistive effect device 10, straincan be introduced by a lattice mismatch between the layers of thestacked body 19. In addition, strain can be introduced by generatinginternal stress between the layers of the stacked body 19 by differencesin thermal expansion. It is considered that the most controlled state isthat due to an external stress. By using an external stress, it ispossible to apply stress in the necessary part of the magneto-resistiveeffect device 10, and this is desirable state from the point of view ofcontrollability.

The configuration of the magnetic head according to this embodiment hasa current-perpendicular-to-plane (CPP) structure in which a sensecurrent flows in a direction perpendicular to the film face of thestacked body 19. However, a current-in-plane (CIP) structure may be usedin which electrodes are disposed on side surfaces of the stacked body19, for example, the side surfaces apart from the ABS surface 23 and theopposite surface thereto, and sense current flows in the in-planedirection along the stacking surfaces.

Next, operation of the magnetic head according to the second embodimentwill be described.

FIGS. 4A through 4C illustrate the magnetization directions of themagneto-resistive effect device, FIG. 4A illustrates a case where thereis no external magnetic field, FIG. 4B illustrates a case where anexternal magnetic field is directed away from the device, and FIG. 4Cillustrates a case where an external magnetic field is directed towardsthe device.

As illustrated in FIG. 4A, a tensile strain 24 is applied to the stackedbody 19 of the magneto-resistive effect device 10 of the magnetic head20, in a direction 45° from the ABS surface 23 when viewed from the topsurface of the stacked body 19. An external magnetic field is appliedfrom a direction normal to the ABS surface 23. Therefore, the tensilestrain 24 is applied from a direction of 45° or 135° when viewed fromthe direction that the external magnetic field is applied. As statedabove, the ferromagnetic layer 11 has a positive magnetostrictioncoefficient, and the ferromagnetic layer 12 has a negativemagnetostriction coefficient.

First a case in which there is no magnetic field due to an externalmagnetic field is explained. The magnetization direction of theferromagnetic layer 11 is a magnetization direction 25 along thedirection of the tensile strain 24 at −135° from the ABS surface 23,when viewed from the top surface of the stacked body 19. With the ABSsurface 23 as reference, counterclockwise is the rotation direction thatincreases the angle, and with the ABS surface 23 as reference, clockwiseis the rotation direction that reduces the angle. On the other hand, themagnetization direction of the ferromagnetic layer 12 is a magnetizationdirection 26 that is normal to the direction of the tensile strain 24,at −45° from the ABS surface 23. In this case, the magnetizationdirections 25 and 26 of the two magnetic layers are mutually orthogonal.Therefore, the resistance state of the magneto-resistive effect device10 is the intermediate state, as a result the operation of a normalspin-valve film. In this embodiment, a case in which a tensile strain isapplied is described, but a compressive strain may also be applied.

Next, a case where an external magnetic field is applied is explained.

As illustrated in FIG. 4B, when an external magnetic field 27 due to anexternal magnetic flux is applied in a direction away from the device,in other words in a direction 27 at −90° from the ABS surface 23, whenviewed from the top surface of the stacked body 19, the magnetizationdirections of the two magnetic layers rotate to approach the direction27 of the external magnetic field. Therefore, the magnetizationdirections of the two magnetic layers become magnetization directions 28and 29. As a result, the magnetization directions of the two magneticlayers approach parallel. In this way, the resistance state of themagneto-resistive effect device 10 is changed to approach the lowresistance state.

In contrast, as illustrated in FIG. 4C, when an external magnetic field30 due to an external magnetic flux is applied in a direction 30 towardsthe device, in other words in a direction 30 at 90° from the ABS surface23, when viewed from the top surface of the stacked body 19, themagnetization directions of the two magnetic layers are rotated by theexternal magnetic field 30 to approach, and become magnetizationdirections 31 and 32. As a result, they tend to be aligned antiparallel.In this way, the resistance state of the magneto-resistive effect device10 is changed to approach the high resistance state.

In FIGS. 4A through 4C, the magnitudes of the normal component and thehorizontal component of the magnetization directions of the two magneticlayers of the magneto-resistive effect device 10 with respect to the ABSsurface 23 were equal.

Next, a case will be explained in which the magnitudes of the normalcomponent and the horizontal component of the magnetization directionsof the two magnetic layers of the magneto-resistive effect device 10with respect to the ABS surface 23 are different.

FIGS. 5A through 5C illustrate the magnetization directions of themagneto-resistive effect device, FIG. 5A illustrates a case where thereis no external magnetic field, FIG. 5B illustrates a case where anexternal magnetic field is directed away from the device, and FIG. 5Cillustrates a case where an external magnetic field is directed towardsthe device.

In the examples illustrated in FIGS. 5A through 5C, the ferromagneticlayer 11 has a positive magnetostriction coefficient, and theferromagnetic layer 12 has a negative magnetostriction coefficient.

As illustrated in FIG. 5A, a tensile strain 33 is applied to the stackedbody 19 of the magneto-resistive effect device 10 of the magnetic head20, in a direction between 0 to 45° from the ABS surface 23 when viewedfrom the top surface of the stacked body 19. First a case in which thereis no magnetic field due to an external magnetic flux is explained. Themagnetization direction of the ferromagnetic layer 11 is rotated alongthe direction of the tensile strain 33, in a direction 34 between −135to −180° from the ABS surface 23, when viewed from the top surface ofthe stacked body 19. On the other hand, the magnetization direction ofthe ferromagnetic layer 12 is rotated normal to the direction of thetensile strain 33, in a direction between −45 to −90° from the ABSsurface 23. In this case, the magnetization directions 34 and 35 of thetwo ferromagnetic layers are orthogonal. Therefore, the resistance stateof the magneto-resistive effect device is the intermediate state, as aresult of the operation of a normal spin-valve film.

Next, a case where an external magnetic field is applied is explained.

As illustrated in FIG. 5B, when an external magnetic field 36 due to anexternal magnetic flux is applied in a direction away from the device10, in other words in a direction at −90° from the ABS surface 23, whenviewed from the top surface of the stacked body 19, the magnetizationdirections of the two ferromagnetic layers rotate to approach closer tothe external magnetic field 36, becoming the magnetization directions 37and 38. As a result, they tend to be aligned closer to parallel. In thisway, the resistance state approaches the low resistance state. Incontrast, as illustrated in FIG. 5C, when an external magnetic field 39due to an external magnetic flux is applied in a direction towards thedevice, in other words in a direction 90° from the ABS surface 23, whenviewed from the top surface of the stacked body 19, the magnetizationdirections of the two magnetic layers are rotated by the externalmagnetic field 39 to approach closer, and become magnetizationdirections 40 and 41. As a result, they tend to be aligned closer toantiparallel. In this way, the resistance state approaches the highresistance state.

As explained above, as long as the magnetization directions of the twoferromagnetic layers have components normal to the direction of anexternal magnetic field, it is possible to detect the external magneticfield by the changes in the resistance state by the spin-valve film.Also, in order that both the magnetization directions of the twoferromagnetic layers have a component normal to the direction of theexternal magnetic field, the magnetization directions of the twoferromagnetic layers may be configured so as to intersect. Then, the twoferromagnetic layers in this embodiment have positive and negativemagnetostriction coefficients, so if a strain in a direction normal tothe stacking direction of the stacked body is introduced into thestacked body, the magnetization directions of the two ferromagneticlayers intersect. Hence it is possible to detect external magneticfields.

In other words, setting the angle θ between the magnetization of the twoferromagnetic layers with the spacer layer disposed therebetween toapproximately 90 degrees is the most preferable state for stability ofoperation of the device. At least, it is necessary that the angle θ beset in the range 0 degrees<θ<180 degrees.

Next, a case in which an external magnetic field is continuouslychanging between the external magnetic field 27 whose direction is awayfrom the device and the external magnetic field 30 whose direction istowards the device is explained, as an example of reading a magneticmedium.

First, the tensile strain 24 as illustrated in FIG. 4A is introduced,with the magnetization directions of the two ferromagnetic layersintersecting as in the magnetization directions 25 and 26. Then, a sensecurrent is passed between electrodes 20 and 21. As stated above, theresistance state is detected to be the intermediate resistance state.

Then, as the magnetic medium moves, if the resistance becomes lower, asillustrated in FIG. 4B, it is determined that the magnetizationdirections of the two ferromagnetic layers have approached parallel.Therefore, “1” is read as the external magnetic field 27 recorded on themagnetic medium below the ABS surface 23 of the magnetic head.

On the other hand, as the magnetic medium moves, if the resistancebecomes high, as illustrated in FIG. 4C, it is determined that themagnetization directions of the two ferromagnetic layers have approachedantiparallel. Therefore, “0” is read as the external magnetic field 30recorded on the magnetic medium below the ABS surface 23 of the magnetichead.

Next, the effect of the magnetic head according to the second embodimentwill be described.

In the magnetic head according to the second embodiment, theferromagnetic layer with the positive magnetostriction coefficient andthe ferromagnetic layer with the negative magnetostriction coefficientare stacked with the spacer layer disposed therebetween, in addition, byapplying a strain to the stacked body 19, it is possible to apply a biasin different directions to the two free layers, so it is possible todetect external magnetic fields. Therefore, it is possible to realize amagnetic head suitable for high densification.

Third Embodiment

Next, a magnetic head according to a third embodiment will be described.

FIG. 6 is a perspective view illustrating the magnetic head according tothe third embodiment.

This embodiment is an example in which a strain introduction member 42is connected to the device, in order to apply the strain introduced intothe magneto-resistive effect device in a more controlled manner.

As illustrated in FIG. 6, in this embodiment, the strain introductionmember 42 is provided adjacent to the magneto-resistive effect device10, for example, on the surface of the stacked body 19 opposite the ABSsurface 23. The strain introduction member 42 may be a part of anenclosure made from an insulating material used as a shield toelectrically isolate or magnetically isolate the device. An internalstress is formed within the stacked body 19 by a mechanical property ofthe strain introduction member 42, for example, by thermal expansion ofthe strain introduction member 42. In this case, the strain is appliedby using materials with different thermal expansion coefficients for thedevice part and the strain introduction member 42. Another example is touse a crystallographic mismatch between the stacked body 19 and thesurrounding substance as the strain introduction member 42. Also,magnetostrictive expansion using a magnetic material havingmagnetostrictive properties can be used.

The strain introduced may be a compressive strain or a tensile strain.

Next, the effect of the magnetic head according to the third embodimentwill be described.

In this embodiment, it is possible to apply strain to the device 10 in acontrolled manner by introducing the strain introduction member 42 intothe magneto-resistive effect device 10, so it is possible to control thebias of the magnetization directions of the two ferromagnetic layerswith the spacer layer disposed therebetween.

In this way, it is possible to realize appropriate magnetization bias inthe magneto-resistive effect device 10 with a thin film thicknesssuitable for narrow gaps. In other words, it is possible to realize amagnetic head suitable for high densification.

Fourth Embodiment

Next, a magnetic head according to a fourth embodiment will bedescribed.

FIGS. 7A and 7B are perspective views illustrating the magnetic headaccording to the fourth embodiment, and FIG. 7C is a cross-sectionalview at the plane A-A′ indicated on FIG. 7B.

As illustrated in FIG. 7A, in this embodiment, a piezoelectric materialis used in the strain introduction member 42.

In order to apply a more actively controlled strain, rather than apassive strain application means such as the above thermal expansion, apiezoelectric material whose crystal deforms with the application of avoltage can be used as the strain introduction member 42.

The following materials are examples of specific materials having thistype of voltage characteristic. Namely, silicon oxide (SiO₂), zinc oxide(ZnO), KaC₄H₄O₆, lead zirconate titanate (PZT: Pb(Zr, Ti)O₃), lithiumniobate (LiNbO₃), lithium tantalate (LiTaO₃), lithium borate (Li₂B₄O₇),langasite (La₃Ga₅SiO₁₄), aluminum nitride (AlN), polyvinylidenedifluoride (PVDF), gallium phosphate (GaPO₄), tourmaline, and so on.Also, additive elements or the like may be added to these piezoelectricmaterials as a base, to enhance their characteristics. In the case ofthese piezoelectric materials, the strain introduction member 42includes electrodes 199 a and 199 b to apply a voltage to the strainintroduction member 42, and by applying a voltage to them, it ispossible to apply the strain.

For example, in the strain introduction member 42, the electrodes areprovided on the surface on the opposite side of the surface in contactwith the stacked body 19 of the device 10, and it is possible to applythe strain by applying a voltage.

These materials have insulating properties, so they can be brought intocontact with the stacked body 19 of the device 10. By bringing thedevice and the strain introduction member directly into contact, it ispossible to apply a greater strain.

In FIG. 7A, the electrodes 119 a, 119 b are disposed in locations on thestrain introduction member 42 in order to apply the voltage, but theelectrodes can be disposed in other locations. For example, asillustrated in FIG. 2C, if a straight line 302 normal to the directionof application of the external magnetic field 301 to themagneto-resistive effect device 10 is taken to be 0 degrees, when viewedfrom above the film face, when the angle θ between a tensile stress or acompressive stress and the straight line 302 is 45 degrees or 135degrees, it is possible to realize an appropriate bias. Therefore, theelectrodes for applying stress to the strain introduction member 42 arepreferably provided at one end of the piezoelectric member, asillustrated in FIGS. 7B and 7C. In other words, when the straight line302 normal to the direction of application of the external magneticfield 301 is taken to be 0 degrees, an electrode 119 c is provided in aposition at 45 degrees or 135 degrees when viewed from above the filmface, a position that is capable of applying a stress to themagneto-resistive effect device 10 in a direction 45 degrees or 135degrees when viewed from the ABS surface 23.

Next, the effect of the magnetic head according to the fourth embodimentwill be described.

In this embodiment, a piezoelectric material is used as the strainintroduction member 42, so it is possible to introduce an activelycontrolled strain, and it is possible to realize a magnetic headsuitable for high density.

Fifth Embodiment

Next, a magnetic head according to a fifth embodiment will be described.

FIG. 8 is a perspective view illustrating the magnetic head according tothe fifth embodiment.

As illustrated in FIG. 8, in this embodiment, an insulating material 45is provided between the strain introduction member 42 and the stackedbody 19.

The piezoelectric material has inferior insulating properties comparedwith silicon oxide (SiO₂) with an amorphous structure, aluminum oxide(Al₂O₃) with an amorphous structure, and so on, that are normally usedas the insulating material of the device 10, so after providing thesecommon insulating materials around the device, the strain introductionmember 42 is placed in contact with the outside thereof, with about 1 to3 nm therebetween. Between the strain introduction member 42 and thestacked body 19, silicon oxide (SiO₂), aluminum oxide (Al₂O₃) is placedin contact. In each case, the strain introduction member 42 can beconsidered to be a bias application structure for controlling themagnetization directions of the two ferromagnetic layers 11 and 12 ofthe stacked body 19 of the device 10. In other words, in contrast to aconventional hard bias, in which the magnetization direction of themagnetic layer is controlled with a bias using a magnetic field, in thisembodiment, a magnetic field is not used, but by using strain, which isa different physical quantity, it is possible to orient themagnetization of the two ferromagnetic layers 11 and 12 in differentdirections.

In this way, the bias to orient the magnetization directions of the twomagnetic layers in different directions using a magnetic field wasinevitably very difficult and complex, so realization was difficult. Incontrast, in the method of this embodiment, by providing the top andbottom magnetic layers with opposite magnetostriction polarity, with thespacer layer disposed therebetween, and applying an external strain ofsingle polarity, it is possible to bias the magnetization directions ofthe two ferromagnetic layers in different directions.

The effect of the magnetic head according to this embodiment is the sameas described above, so the explanation is omitted.

Sixth Embodiment

Next, a magnetic head according to a sixth embodiment will be described.

FIG. 9 is a perspective view illustrating the magnetic head according tothe sixth embodiment.

As illustrated in FIG. 9, in this embodiment, the strain introductionmember 42 is located on the two side surfaces of the stacked body 19,apart from the ABS surface 23 and the surface opposite the ABS surface23, with the stacking direction of the stacked body 19 taken to bevertical. Then, the stacked body 19 and the strain introduction members42 are sandwiched between the top electrode 21 and the bottom electrode22 in the vertical direction of the stacked body 19. In other words, thestrain introduction members 42 are provided instead of a conventionalhard bias film. A piezoelectric material can be used. Specific examplesof the piezoelectric material in this case are the same as thosematerials previously described.

If necessary, in addition to the method of biasing by applying strainaccording to this embodiment, it is possible to provide a hard bias filmusing a magnetic field to bias the magnetization of the ferromagneticlayers 11 and 12 in accordance with the circumstances. In this case, ahybrid bias structure can be considered, in which a hard bias layer isdisposed in the same location as when using a magnetic field, and thestrain introduction members 42 are provided to the left and rightseparated from the hard bias film, when viewed from the ABS surface 23.

The effect of the magnetic head according to this embodiment is the sameas described above, so the explanation is omitted.

Seventh Embodiment

Next, a magnetic head according to a seventh embodiment will bedescribed.

FIG. 10 is a perspective view illustrating the magnetic head accordingto the seventh embodiment.

As illustrated in FIG. 10, in this embodiment, the strain introductionmember 42 is inserted between the stacked body 19 and the bottomelectrode 22. The strain introduction member 42 may also be insertedbetween the stacked body 19 and the top electrode 21.

In the case of FIG. 10, the strain introduction member 42 is used incombination with the electrode to pass current through the stacked body19 of the device 10. Therefore a piezoelectric material is not suitableas the strain introduction member 42.

Next, operation of the magnetic head according to the seventh embodimentwill be described.

In this embodiment, the strain introduction member 42 is insertedbetween the stacked body 19 and the electrode in order to furtherincrease the strain introduced into the magneto-resistive effect device10. A characteristic strain is generated in the device by the strainintroduction member 42. Also, the strain introduction member 42 causes astrain in the device as an external factor. The strain introductionmember 42 is stacked on the stacked body 19, so it is possible tointroduce more strain in the in-plane direction.

The device characteristic strain and the strain due to external factorare the same as described for the third embodiment, so the explanationis omitted here.

Eighth Embodiment

Next, a magnetic head according to an eighth embodiment will bedescribed.

FIG. 11 is a perspective view illustrating the magnetic head accordingto the eighth embodiment. The difference between the seventh embodimentand the eighth embodiment is that, in the seventh embodiment, the strainintroduction member 42 is a single layer, and in contrast in the eighthembodiment there are two layers, disposed between the stacked body 19and each of the pair of electrodes.

As illustrated in FIG. 11, in the eighth embodiment, the strainintroduction member 42 is inserted between the stacked body 19 and thetop electrode 21, and between the stacked body 19 and the bottomelectrode 22.

In the case of FIG. 11, the strain introduction members 42 are used incombination with the electrodes to pass current through the stacked body19, so an insulating material cannot be used. Therefore a piezoelectricmaterial is not suitable as the strain introduction member 42.

Next, operation of the magnetic head according to the eighth embodimentwill be described.

In the eighth embodiment also, a strain introduction member 42 isinserted between the stacked body 19 and each of the pair of electrodesin order to further increase the strain introduced into themagneto-resistive effect device. A characteristic strain is generated inthe device by the strain introduction members 42. Unlike the seventhembodiment, both the first and second magnetic layers are in contactwith the strain introduction members 42.

The device characteristic strain and the strain due to external factorare the same as described above.

Ninth Embodiment

Next, a magnetic head according to a ninth embodiment will be described.

FIG. 12 is a perspective view illustrating the magnetic head accordingto the ninth embodiment.

As illustrated in FIG. 12, in this embodiment, the magneto-resistiveeffect device 10 is provided on a substrate 43 a. In other words, thebottom electrode 22 is provided on the substrate 43 a, and the stackedbody 19 is provided on the bottom electrode 22. The top electrode 21 isprovided on the stacked body 19.

Next, operation of the magnetic head according to the ninth embodimentwill be described.

In this embodiment, the magneto-resistive effect device 10 is providedon the substrate 43 a. The substrate 43 a may be the strain introductionmember 42. For example, if the magneto-resistive effect device 10 isformed on the substrate 43 a after introducing a strain into thesubstrate 43 a, strain is introduced into the stacked body 19.

Next, the effect of the magnetic head according to the ninth embodimentwill be described.

In the ninth embodiment, the substrate 43 a can be the strainintroduction member 42, so there is no necessity to provide a dedicatedstrain introduction member 42 as in the first through third variations,so the magnetic head can be miniaturized.

Tenth Embodiment

Next, a tenth embodiment will be described. This embodiment relates to amagnetic head gimbal assembly.

FIGS. 13A and 13B are perspective views illustrating the magnetic headgimbal assembly according to the tenth embodiment.

As illustrated in FIG. 13A, a head stack assembly 160 includes a bearingpart 157, a magnetic head gimbal assembly 158 extending from the bearingpart 157, and a support frame 161 extending from the bearing part 157 ina direction opposite that of the magnetic head gimbal assembly 158 andthat supports a coil 162 of a voice coil motor.

Also, as illustrated in FIG. 13B, the magnetic head gimbal assembly 158includes an actuator arm 155 extending from the bearing part 157, and asuspension 154 extending from the actuator arm 155. A head slider 3 ismounted on a tip of the suspension 154. Then the magnetic head accordingto the embodiment is mounted on the head slider 3. In other words, themagnetic head gimbal assembly 158 according to this embodiment includesthe magnetic head according to the embodiment, the head slider 3 intowhich the magnetic head is mounted, the suspension 154 mounted at oneend of the head slider 3, and the actuator arm 155 connected to theother end of the suspension 154. The suspension 154 includes leads (notillustrated on the drawings) for writing and reading signals, for aheater for adjusting the floating height, and for a spin torqueoscillator, for example, and so on. These leads are electricallyconnected to the electrodes of the magnetic head incorporated into thehead slider 3.

Eleventh Embodiment

FIG. 14 is a perspective view illustrating the magneticrecording/reproduction device according to an eleventh embodiment.

As illustrated in FIG. 14, a magnetic recording/reproduction device 150according to the eleventh embodiment is a rotary actuator-type device.In this drawing, a recording medium disk 180 is mounted on a spindlemotor 4, and is rotated in the direction of the arrow symbol A by amotor, which is not illustrated on the drawings, in response to acontrol signal from a drive device control unit, which is notillustrated on the drawings. The magnetic recording/reproduction device150 according to this embodiment may include a plurality of recordingmedium disks 180. The head slider 3 that records and reproducesinformation stored on the recording medium disk 180 is mounted on thetip of the suspension 154 in thin film form. Here, a magnetic headaccording to any of the embodiments that have been already explained,for example, is mounted near the tip of the head slider 3.

When the recording medium disk 180 rotates, the pressing pressure fromthe suspension 154 and the pressure generated by the media opposing face(ABS) of the head slider 3 balance, and the media opposing face of thehead slider 3 is maintained at a predetermined floating height from thesurface of the recording medium disk 180. The contact between the headslider 3 and the recording medium disk 180 may be “moving contact type”.

The suspension 154 is connected to a first end of the actuator arm 155which has a bobbin portion or the like for supporting a drive coil (notillustrated). A voice coil motor 156, which is a type of linear motor,is provided on a second end of the actuator arm 155. The voice coilmotor 156 can include a drive coil (not illustrated) that is woundaround the bobbin portion of the actuator arm 155, and a magneticcircuit with a permanent magnet and a counter yoke which are disposedopposite to one another so as to sandwich the drive coil.

The actuator arm 155 is supported by ball bearings (not illustrated)provided at two locations, at the top and bottom of the bearing part157, and thereby the actuator arm 155 can be rotated and slid freely bythe voice coil motor 156. As a result, it is possible to move themagnetic head to any position on the recording medium disk 180.

Also, a signal processing unit 190 that writes and reads signals to andfrom the magnetic recording media using the magnetic head is provided.The signal processing unit 190 is provided on the reverse side (of thedrawing) of the magnetic recording/reproduction device 150. Input andoutput wires of the signal processing unit 190 are connected to anelectrode pad of a magnetic head gimbal assembly that constitutes a partof the head stack assembly 160, and is thereby electrically connected tothe magnetic head.

The magnetic recording/reproduction device 150 according to thisembodiment uses the head gimbal assembly 158 that includes a magnetichead that includes the magneto-resistive effect device as describedabove, manufactured in accordance with at least any of the first throughthird embodiments of the invention, so it can reliably read informationrecorded magnetically on a magnetic disk 200 at high memory density,using the MR rate of change.

Twelfth Embodiment

Next, a twelfth embodiment will be described.

This embodiment relates to a strain sensor.

FIG. 15 is a cross-sectional view illustrating the strain sensoraccording to the twelfth embodiment.

As illustrated in FIG. 15, in the strain sensor according to thisembodiment, a flexible substrate 43 is provided. A priming layer 44 isprovided on the flexible substrate 43. The priming layer 44 may beconfigured from a plurality of layers such as seed layers (notillustrated) or pinning layers (not illustrated). These several layerscan be omitted by using a special thin film structure. By providing thepriming layer 44, it is possible to suppress defects that are notnecessary for the flexible substrate 43, for example, surface roughness.Also, by providing the seed layers, it is possible to control theimportant crystal direction for forming the magnetic layer/spacerlayer/magnetic layer. In addition, by providing the pinning layers, itis possible to fix the magnetization direction of a pinned layer. Thepriming layer 44 may be a conductive material.

The bottom electrode 22 is provided on the priming layer 44, and themagneto-resistive effect device 10 with the stacked body 19 structure isprovided thereupon. The magneto-resistive effect device 10 is the sameas the magneto-resistive effect device according to the firstembodiment, so it is configured from the ferromagnetic layer 11, theferromagnetic layer 12, and the spacer layer 13 disposed between theferromagnetic layer 11 and the ferromagnetic layer 12. The polarities ofthe magnetostriction of the ferromagnetic layer 11 and the ferromagneticlayer 12 are positive and negative, constituted from materials withdifferent polarity magnetostriction coefficient. However, theferromagnetic layer 11 and the ferromagnetic layer 12 have oppositemagnetostrictive effects. In other words, one of the ferromagnetic layer11 and the ferromagnetic layer 12 is a ferromagnetic layer with apositive magnetostriction coefficient, and the other is a ferromagneticlayer with a negative magnetostriction coefficient.

The top electrode 21 is provided on the stacked body 19, forming a CPPstructure in which current flows in the stacking direction of thestacked body. In other words, the sense current flows vertically throughthe stacked body.

In other to protect the magneto-resistive effect device 10, and in orderto electrically isolate the magneto-resistive effect device 10 fromother members, the periphery of the magneto-resistive effect device 10is covered with an insulating material 45.

The following are specific examples of materials with differentmagnetostriction polarity of the ferromagnetic layer 11 and theferromagnetic layer 12 of the magneto-resistive effect device 10.

Normally, the magnetostriction of a magnetic layer is determined by thecomposition of the magnetic layer. The general trends of these have beeninvestigated in many publications. However, the actual magnetostrictionis greatly affected by the materials adjacent to the magnetic layer.

If an oxide material is used as the spacer layer (a tunnel barrier layersuch as magnesium oxide (MgO) or a CCP layer), when a magnetic layerthat includes cobalt iron (CoFe) or the like is used at the interfacewith the spacer layer, the top and bottom magnetic layers normally havepositive magnetostriction within 1 to 2 nm of the interface. This isbecause magnetic oxide layers such as CoFeBO_(x), CoO_(x), NiO_(x) andFeO_(x), and so on are materials that have positive magnetostriction.Next, the ferromagnetic layers 11 and 12 are given different positiveand negative magnetostriction. It is comparatively easy to form aferromagnetic layer with positive magnetostriction. Therefore, in orderto form negative magnetostriction, by stacking a magnetic layer withlarge negative magnetostriction onto the oxide interfacial layer of theoxide layer that has positive magnetostriction, the magnetic layer withnegative magnetostriction can be formed as the total magnetic layer.Large negative magnetostriction can be achieved using a nickel (Ni) richalloy. Examples include Ni, NiFe alloy (including not less than 85atomic percent Ni), SmFe, and so on. When the magnetic material isformed from a plurality of layers so that they act as a magneticallyintegral magnetic layer, the magnetostriction of the magnetic layer isdetermined by the total stacked film constitution of the magnetic layers(on the other hand, the other magnetic layer with the nonmagnetic layerdisposed therebetween functions as a separate magnetic layer, so themagnetostriction is defined as a separate value).

A specific example of the stacked film constitution of the ferromagneticlayer 11/spacer layer 13/ferromagnetic layer 12 is a stacked film ofCo₉₀Fe₁₀/CoFeB/MgO/CoFeB/Ni₉₅Fe₅, with film thicknesses of 2 nm/1 nm/1.5nm/1 nm/2 nm respectively. Here, the Co₉₀Fe₁₀/CoFeB layers function as asingle ferromagnetic layer that exhibits positive magnetostriction, andthe CoFeB/Ni₉₅Fe₅ layers function as a single ferromagnetic layer thatexhibits negative magnetostriction. The MgO layer is the spacer layer.

Next, operation of the strain sensor according to the twelfth embodimentwill be described.

FIGS. 16 and 17 are cross-sectional views illustrating the operation ofthe strain sensor according to the twelfth embodiment.

As illustrated in FIG. 16, when an upward acting stress 48 is applied tothe flexible substrate 43, the outside of the flexible substrate 43 isstretched and rounded, and as a result a tensile strain 49 is applied tothe magneto-resistive effect device 10 fixed to the flexible substrate43.

On the other hand, as illustrated in FIG. 17, when a downward actingstress 51 is applied to the flexible substrate 43, the flexiblesubstrate 43 is bent to the inside, and as a result a compressive strain52 is applied to the device 10.

FIGS. 18A and 18B illustrate the operation of the strain sensoraccording to the twelfth embodiment, FIG. 18A illustrates a case inwhich a tensile strain is applied, and FIG. 18B illustrates a case inwhich a compressive strain is applied.

FIGS. 18A and 18B illustrate only the two ferromagnetic layers of themagneto-resistive effect device 10.

As stated above, the stacked body 19 is disposed in the strain sensoraccording to the twelfth embodiment, and the stacked body 19 includesthe ferromagnetic layer 11 and the ferromagnetic layer 12.

As illustrated in FIGS. 18A and 18B, in the magneto-resistive effectdevice 10, of the two ferromagnetic layers, the top layer is theferromagnetic layer 11 with a positive magnetostriction coefficient, andthe bottom layer is the ferromagnetic layer 12 with a negativemagnetostriction coefficient. Also, prior to application of the strain,the magnetization directions 65 and 66 of the ferromagnetic layers 11and 12 are parallel. In other words, the resistance state of the device10 is the low resistance state. Then, as illustrated in FIG. 18A, when atensile strain 63 is applied to the device in the same direction as themagnetization directions 65 and 66, the magnetization direction 65 ofthe ferromagnetic layer 11 does not change, but the magnetizationdirection 66 of the ferromagnetic layer 12 changes to a magnetizationdirection 67 normal to the tensile strain. As a result, themagnetization directions of the two ferromagnetic layers becomeorthogonal to each other. Then the resistance state of the device 10changes to the intermediate resistance state.

Also, as illustrated in FIG. 18B, when a compressive strain 68 isapplied to the device 10 in the same direction as the magnetizationdirections 65 and 66, the magnetization direction 65 of theferromagnetic layer 11 changes to a magnetization direction 70 normal tothe compressive strain, but the magnetization direction 66 of theferromagnetic layer 12 does not change. As a result, the magnetizationdirections of the two ferromagnetic layers become orthogonal to eachother. Then the resistance state of the device 10 changes to theintermediate resistance state.

Next, the method of measuring the magnitude of the strain using thestrain sensor is explained.

First, the strain sensor is placed on the location where the strain isto be measured. Prior to application of the strain to the strain sensor,the magnetization directions of the ferromagnetic layers 11 and 12 areparallel. Then, the sense current is passed between the electrodes 20and 21, to determine the resistance state of the stacked body 19. Asstated previously, as long as there is no strain applied to the strainsensor, the resistance state of the stacked body 19 will be the lowresistance state.

Next, it is assumed that the resistance state becomes the intermediateresistance state. In this case, it can be determined that themagnetization direction of the ferromagnetic layer 11 and themagnetization direction of the ferromagnetic layer 12 of the stackedbody 19 have changed to become orthogonal. In other words, it can bedetermined that a strain has been applied to the substrate 43 sufficientto make the magnetization direction of the ferromagnetic layer 11 andthe magnetization direction of the ferromagnetic layer 12 orthogonal.The resistance state changes in accordance with the angle between themagnetization direction of the ferromagnetic layer 11 and themagnetization direction of the ferromagnetic layer 12. Therefore, if therelationship between the resistance state and the amount of strainapplied to the substrate 43 is determined in advance by another method,it is possible to measure the amount of strain applied to the substrate43 by measuring the magnitude of the sense current.

In FIGS. 18A and 18B, the directions of application of the tensilestrain and the compressive strain are the same as the magnetizationdirections of the ferromagnetic layers, but are not limited thereto.

The direction of the strain is not important for exhibiting the functionof the magneto-resistive effect device 10. This is because theresistance state changes for any strain direction.

FIGS. 19A, 19B, and 19C illustrate the operation of the strain sensoraccording to the twelfth embodiment, FIG. 19A illustrates a case inwhich a tensile strain is applied in an arbitrary direction, FIG. 19Billustrates a case in which a compressive strain is applied in anarbitrary direction, and FIG. 19C illustrates a case in which acompressive strain is applied and prior to application of the strain themagnetization directions of the two ferromagnetic layers areantiparallel.

As illustrated in FIG. 19A, when a tensile strain 71 is applied to thedevice 10 at an arbitrary angle to the magnetization directions of theferromagnetic layer 11 and the ferromagnetic layer 12, the magnetizationdirection 65 of the ferromagnetic layer 11 rotates towards the directionof the tensile strain and changes to the magnetization direction 73, andthe magnetization direction 66 of the ferromagnetic layer 12 rotatesorthogonal to the direction of the tensile strain and changes to themagnetization direction 74. As a result, the magnetization directions ofthe two ferromagnetic layers become orthogonal to each other. Then theresistance state of the device 10 changes to the intermediate resistancestate.

Also, as illustrated in FIG. 19B, when a compressive strain 75 isapplied to the device 10 at an arbitrary angle to the magnetizationdirections of the ferromagnetic layer 11 and the ferromagnetic layer 12,the magnetization direction 65 of the ferromagnetic layer 11 rotatesorthogonal to the direction of the compressive strain and changes to themagnetization direction 77, and the magnetization direction 66 of theferromagnetic layer 12 rotates towards the direction of the compressivestrain and changes to the magnetization direction 78. As a result, themagnetization directions of the two ferromagnetic layers becomeorthogonal to each other. Then the resistance state of the device 10changes to the intermediate resistance state.

In this way, the resistance state of the device 10 changes with a strainin an arbitrary direction, so it is possible to detect the magnitude ofthe strain.

Also, even when the initial state of the magnetization directions of thetwo ferromagnetic layers prior to application of the strain isantiparallel, it is possible to detect the strain of the substrate 43.

As illustrated in FIG. 19C, the initial magnetization directions 79 and80 of the ferromagnetic layer 11 and the ferromagnetic layer 12 areantiparallel. In other words, the resistance state of the device 10 isthe high resistance state. Then, for a compressive strain 81 at anarbitrary angle, the magnetization directions 79 and 80 rotate to thedirection orthogonal to and the direction towards the compressive strainrespectively, and change to the magnetization directions 83 and 84. As aresult, the magnetization directions of the two ferromagnetic layersbecome orthogonal to each other. Then the resistance state of the device10 changes to the intermediate resistance state. Hence, the initialmagnetization directions of the ferromagnetic layers are not importantfor exhibiting the function of the magneto-resistive effect device 10.

Next, the effect of the strain sensor according to the twelfthembodiment will be described.

The strain sensor according to this embodiment can detect either atensile strain or a compression strain. Also, it is possible to detectstrain at an arbitrary angle to the magnetization direction of themagneto-resistive effect device 10 of the strain sensor. Also, it ispossible to detect strain regardless of the initial magnetizationdirection of the magneto-resistive effect device, so it is possible tobroaden the options for material of the ferromagnetic layers. Therefore,a single strain sensor according to this embodiment can detect strain asdescribed above, so miniaturization is possible.

Variation of the Twelfth Embodiment

Next, a variation of the strain sensor according to a twelfth embodimentwill be described.

FIG. 20 is a cross-sectional view illustrating the variation of thestrain sensor according to the twelfth embodiment.

As illustrated in FIG. 20, in this variation, electrodes 46, 47 areprovided on two sides sandwiching the stacked body 19.

Therefore, the sense current flows in the in-plane direction of thestacked body. In this embodiment, the device is covered with insulatingmaterial from above. The configuration, operation and effect of thisembodiment other than that described above is the same as the thirdembodiment as described previously.

Thirteenth Embodiment

Next, a strain sensor according to a thirteenth embodiment will bedescribed.

FIG. 21 is a cross-sectional view illustrating the strain sensoraccording to the thirteenth embodiment.

As illustrated in FIG. 21, the strain sensor according to thisembodiment includes at least two magneto-resistive effect devices A, B.The two devices A, B are formed at two locations on a circular shapedmembrane 85. The locations are such that the distances from the centerof the circular shape to the two fixing locations are equal, and theangle between the directions from the center of the circular shapetowards the two fixing locations is 90°. In other words, as illustratedin FIG. 21, one device A is provided at a location 86 at 3 o'clock on aclock viewed from above the circular shaped membrane 85, and the otherdevice B is provided at a location 87 at 6 o'clock.

In this embodiment, the material of the substrate 43 is, for example, athinly etched silicon that can easily bend. The substrate 43 hasflexibility, and includes the membrane 85 to which the stacked body 19is fixed and a supporting part that supports the membrane 85. However,provided it is possible to provide both the flexible membrane 85 and thesupporting part, a flexible substrate other than silicon as describedlater can be used. Such a material can include ABS resin,cycloolefin-based resin, ethylene-propylene-based rubber, polyamide,polyamide-imide resin, polybenzimidazole, polybutylene terephthalate,polycarbonate, polyethene, PEEK, polyetherimide, polyethylene imine,polyethylene naphthalate, polyester, polysulfone, polyethyleneterephthalate, phenol formaldehyde resin, polyimide, polymethylmethacrylate, polymethylpentene, polyoxymethylene, polypropylene,m-phenyl ether, poly(para-phenylene sulfide), para-aramid, polystyrene,polysulfone, polyvinyl chloride, polytetrafluoroethylene,perfluoroalkoxy, FEP, ETFE, polyethylene chloro trifluoro ethylene,polyvinylidene difluoride, melamine-formaldehyde, liquid crystalpolymer, urea-formaldehyde, and so on.

Controllers 88 are provided around the membrane 85, and the controllers88 are electrically connected to the devices A, B. The resistance statesof the devices A, B are measured by the controllers 88.

Next, operation of the strain sensor according to the thirteenthembodiment will be described.

FIGS. 22A through 22D illustrate the operation of the strain sensor inaccordance with the thirteenth embodiment, FIG. 22A illustrates a casewhere a compressive strain is applied to the device A, FIG. 22Billustrates a case where a tensile strain is applied to the device A,FIG. 22C illustrates a case where a compressive strain is applied to thedevice B, and FIG. 22D illustrates a case where a tensile strain isapplied to the device B.

It is assumed that the strain formed at locations 86 and 87 of thecircular shaped membrane 85 as illustrated in FIG. 21 is virtually inhoop form. As a result, the directions of the strains applied to the twodevices A, B will be mutually orthogonal.

As illustrated in FIGS. 22A and 22C, if compressive strains 89, 91 areapplied to the devices A, B on the membrane 85, the magnetizationdirection 65 of the ferromagnetic layer 11, which has a positivemagnetostriction coefficient, of one of the devices B will rotate in adirection normal to the compressive strain. The magnetization direction66 of the ferromagnetic layer 12, which has a negative magnetostrictioncoefficient, of the other device A will rotate in the opposite direction94. Therefore, the resistance states of the devices A and B will both bethe intermediate resistance state.

On the other hand, if a tensile strain is applied, the opposite responsewould occur. In other words, as illustrated in FIGS. 22B and 22D, iftensile strains 90, 92 are applied to the devices A, B on the membrane85, the magnetization direction 65 of the ferromagnetic layer 11, whichhas a positive magnetostriction coefficient, of one of the devices Awill rotate in a direction 96 towards the tensile strain. Themagnetization direction 66 of the ferromagnetic layer 12, which has anegative magnetostriction coefficient, of the other device B will rotatein the opposite direction 95. Therefore, the resistance states of thedevices A and B will both be the intermediate resistance state.

Next, the effect of the strain sensor according to the thirteenthembodiment will be described.

The strain sensor according to this embodiment can respond to bothcompressive and tensile strains. Therefore it is possible to provide astrain sensor that can be miniaturized. Also, it can function as apressure sensor by enabling the membrane to detect external pressure.

Fourteenth Embodiment

Next, a strain sensor according to a fourteenth embodiment will bedescribed.

FIG. 23 is a perspective view illustrating the strain sensor accordingto the fourteenth embodiment, and FIG. 24 illustrates themagneto-resistive effect device in the strain sensor according to thefourteen embodiments.

As illustrated in FIG. 23, in the strain sensor according to thefourteenth embodiment, a plurality of magneto-resistive effect devices10 is provided on a flexible substrate 107.

Here the flexible substrate 107 is constituted from a flexible thin filmor a flexible sheet that is capable of bending unsymmetrically whenviewed from the top surface. The flexible substrate 107 may be supportedby a support part at the peripheral portion thereof. These substratesare made from a material that can bend, for example a material whosemain component is a polymer. Such a material can include ABS resin,cycloolefin-based resin, ethylene-propylene-based rubber, polyamide,polyamide-imide resin, polybenzimidazole, polybutylene terephthalate,polycarbonate, polyethene, PEEK, polyetherimide, polyethylene imine,polyethylene naphthalate, polyester, polysulfone, polyethyleneterephthalate, phenol formaldehyde resin, polyimide, polymethylmethacrylate, polymethylpentene, polyoxymethylene, polypropylene,m-phenyl ether, poly(para-phenylene sulfide), para-aramid, polystyrene,polysulfone, polyvinyl chloride, polytetrafluoroethylene,perfluoroalkoxy, FEP, ETFE, polyethylene chloro trifluoro ethylene,polyvinylidene difluoride, melamine-formaldehyde, liquid crystalpolymer, urea-formaldehyde, and so on.

As illustrated in FIG. 23, a plurality of word lines 108 that extend ina certain direction and a plurality of bit lines 109 that extend in adirection that intersects the direction of the word lines in a rightangle are provided on the flexible substrate 107.

Also, a plurality of stacked bodies 19 that constitute magneto-resistiveeffect devices 10 is fixed to the flexible substrate 107. The stackedbodies 19 are connected between each of the plurality of word lines 108and each of the bit lines 109. The word lines 108 and the bit lines 109are each electrically connected to a controller 88.

FIG. 24 is a cross-sectional view illustrating the magneto-resistiveeffect device in the strain sensor according to the fourteenthembodiment.

As illustrated in FIG. 24, the word line 108 is connected to the topelectrode 21 of the magneto-resistive effect device 10, and the bit line109 is connected to the bottom electrode 22. In this embodiment, thesense current flows in the stacking direction of the stacked body 19.

Next, operation of the strain sensor according to the fourteenthembodiment will be described.

In the strain sensor according to the fourteenth embodiment, the wordline 108 and the bit line 109 connected to the device 10 at the locationon the flexible substrate 107 that is to be measured are selected usingthe controllers 88, and the resistance state of the device 10 ismeasured by passing sense current through the selected word line 108 andbit line 109. In this way, the magnitude of the strain at the locationwhere the device 10 is positioned is measured.

Next, the effect of the strain sensor according to the fourteenthembodiment will be described.

In the strain sensor according to this embodiment, the plurality ofmagneto-resistive effect devices 10 is provided on the flexiblesubstrate 107. Then, it is possible to detect the local strain at thelocations where the magneto-resistive effect devices 10 are provided.Therefore it is possible to miniaturize the strain sensor by providingdevices 10 that can be miniaturized.

This type of configuration is extremely useful in cases where it is notpossible to properly dispose strain sensors at locations where strain isgenerated. For example, it is extremely useful when used in a bloodpressure sensor that is used in daily life, as described later. In ablood pressure sensor that is used in daily life, the sensor is fittedand removed every day, but it is not easy to apply a small sensor to theproper position of the pulse. However, in the case of a sensor arrayabout the size of an adhesive plaster, it is comparatively easy to applythe array on the pulse. In this case, any sensor on the array canmeasure the pulse, so it is possible to use it for applications in whichmeasurement is extremely difficult, such as measurement of bloodpressure every day.

Fifteenth Embodiment

Next, a fifteenth embodiment will be described.

This embodiment relates to a magneto-resistive effect device.

As stated above, in a strain sensor that uses the magneto-resistiveeffect device 10 according to the first embodiment, it is possible tomeasure the magnitude of both tensile and compressive strains. However,it is not easy to differentiate between a tensile and a compressivestrain.

In the fifteenth embodiment, the above problem is solved with amagneto-resistive effect device to which a third magnetic layer isadded, and that includes two spin-valve films.

FIG. 25 is a perspective view illustrating the magneto-resistive effectdevice according to the fifteenth embodiment.

As illustrated in FIG. 25, a third ferromagnetic layer 97 is provided ina magneto-resistive effect device 110. In other words, the spacer layer13 is provided between the ferromagnetic layer 11 and the ferromagneticlayer 12, and a second spacer layer 98 is provided between theferromagnetic layer 12 and a third ferromagnetic layer 97, to obtain thestructure of a stacked body 99. The third ferromagnetic layer 97functions as a pinned layer. In other words, the pinned layer functionsas a layer whose magnetization direction does not rotate even when astrain is introduced (a pinned reference layer).

Next, operation of the magneto-resistive effect device according to thefifteenth embodiment will be described.

FIGS. 26A and 26B illustrate the stacked body of the magneto-resistiveeffect device according to the fifteenth embodiment, FIG. 26Aillustrates a case of application of a tensile strain, and FIG. 26Billustrates a case of application of a compressive strain.

As illustrated in FIGS. 26A and 26B, in the magneto-resistive effectdevice 110, among the three ferromagnetic layers, the top layer is theferromagnetic layer 11 having a positive magnetostriction coefficient,the middle layer is the ferromagnetic layer 12 having a negativemagnetostriction coefficient, and the bottom layer is the pinned layer97. Also, prior to application of the strain, the magnetizationdirections 65 and 66, and 100 of the ferromagnetic layers 11 and 12 andthe pinned layer 97 are parallel. Therefore, prior to application of thestrain, the resistance state of the device 110 is the low resistancestate.

As illustrated in FIG. 26A, when a tensile strain 101 is applied to thedevice 110 in the same direction as the magnetization directions 65, 66,and 100, the magnetization direction 65 of the ferromagnetic layer 11does not change, but the magnetization direction 66 of the ferromagneticlayer 12 changes to a magnetization direction 103 normal to the tensilestrain 101. As a result, the resistance state between the ferromagneticlayer 11 and the ferromagnetic layer 12 becomes the intermediateresistance state, the resistance state between the ferromagnetic layer12 and the pinned layer 97 becomes intermediate resistance state, andoverall the resistance state of the device 110 is changed to the highresistance state.

Also, as illustrated in FIG. 26B, when a compressive strain 104 isapplied to the device 110 in the same direction as the magnetizationdirections 65, 66 and 100, the magnetization direction 65 of theferromagnetic layer 11 changes to a magnetization direction 106 normalto the compressive strain, but the magnetization direction 66 of theferromagnetic layer 12 does not change. As a result, the resistancestate between the ferromagnetic layer 11 and the ferromagnetic layer 12becomes the intermediate resistance state, the resistance state betweenthe ferromagnetic layer 12 and the pinned layer 97 remains the lowresistance state, and overall the resistance state of the device 110 ischanged to the intermediate resistance state.

In FIG. 26, the directions of application of the tensile strain and thecompressive strain are the same as the magnetization directions of theferromagnetic layers, but this is not a limitation. The important pointis that the magnetization direction of the free layers rotate inopposite directions under the effect of the two types of strain, tensileand compressive.

In this embodiment, there are two spacer layers. One of these, thespacer layer 13, depends on the relative angle between the magnetizationdirections of the two ferromagnetic layers, and the other spacer layer98 depends on the relative angle between the magnetization directions ofthe ferromagnetic layer 12 and the pinned layer 97. Therefore, adifference is produced between the effect of the two types of strain,tensile and compressive.

As illustrated in FIGS. 26A and 26B, in a certain direction a tensilestrain can cause the resistance state to change to the high resistancestate, and in another direction a compressive strain can cause theresistance state to change to the high resistance state.

Next, the effect of the magneto-resistive effect device according to thefifteenth embodiment will be described.

In the magneto-resistive effect device according to this embodiment, itis possible to distinguish whether the applied strain is a tensilestrain or a compressive strain by adding the third ferromagnetic layer,to obtain the magneto-resistive effect device 110 that includes two spinvalves. In this way, it is possible to realize a magneto-resistiveeffect device that is small and is capable of distinguishing thepolarity of the strain. The configuration, operation, and effect of thisembodiment other than that described above is the same as the firstembodiment as described previously.

Sixteenth Embodiment

Next, a sixteenth embodiment will be described.

This embodiment relates to a blood pressure meter.

In this embodiment, a strain sensor according to any of the twelfththrough fifteenth embodiments is applied to a blood pressure sensor.

FIG. 27 is a cross-sectional view illustrating the blood pressure sensoraccording to the sixteenth embodiment.

As illustrated in FIG. 27, a blood pressure sensor 210 is provided at ablood pressure measurement location, and is provided with a part withthe shape of an adhesive plaster 211 for contacting skin surface 213. Inother words, the blood pressure sensor 210 is disposed in contact withthe skin. The blood pressure sensor 210 is disposed on the skin wherethere is an artery directly below. The blood flow direction is thedirection normal to the plane of the paper. The blood flow directionindicates the direction along which the blood vessels extend. If thereis no artery near the surface of the skin, it is difficult to measurethe blood pressure. The locations on the surface of the body where thepulse can be detected (and where there are arteries below the surface)are as follows.

Medial bicipital groove (brachial artery), between the flexor carpiradialis tendon and the brachioradialis tendon at the bottom outerforearm (radial artery), between the flexor carpi ulnaris tendon and thesuperficial digital flexor tendon at the bottom inner forearm (ulnarartery), ulnar extensor pollicis longus muscle tendon (first dorsalmetacarpal artery), armpit (axillary artery), femoral trigone (femoralartery), outside of the tendon of the tibialis anterior at the bottom ofthe front lower leg (anterior tibial artery), lower posterior part ofmedial malleolus (posterior tibial artery), outside of extensor pollicislongus muscle tendon (dorsal artery of foot), carotid artery triangle(common carotid artery), in front of the insertion of the massetermuscle (facial artery), between the trapezius origins posterior to thesternocleidomastoid insertions (occipital artery), in front of theexternal acoustic foramen (superficial temporal artery). Therefore, thelocations at which the blood pressure sensor 210 are disposed are theabove locations. In other words, these correspond to the blood pressuremeasurement locations. The blood pressure sensor 210 is applied to thesurface of the skin at these locations.

Next, operation of the blood pressure sensor according to the sixteenthembodiment will be described.

As illustrated in FIG. 27, when a blood vessel 212 expands in thediametral direction, the skin is pushed up and acts as blood pressure214. At this time, skin that is in the direction normal to the directionthat the blood pressure 214 acts is subject to a tensile stress 215. Atthe same time, it acts on the blood pressure sensor 210 in the directionof the tensile stress 215.

FIG. 28 illustrates the blood pressure sensor according to the sixteenthembodiment.

As illustrated in FIG. 28, the blood pressure of a subject 230 ismeasured using the blood pressure sensor 210. The blood pressure sensor210 is applied to a blood pressure measurement location, for example awrist.

A small battery can be used as the method of supplying electricity tothe blood pressure sensor 210. Also, electricity can be supplied bywireless 250.

The method of accumulating the blood pressure sensor 210 data can betransmission by wireless 250, and accumulation in a mobile phone 240, apersonal computer 260, a wrist watch, or the like.

Next, the effect of the blood pressure sensor according to the sixteenthembodiment will be described.

The blood pressure sensor 210 according to this embodiment includes themagneto-resistive effect device 10 or 110 which is suitable for highdensification, so it can be miniaturized. Therefore it can be used as anubiquitous health monitoring device that can be carried around whilewalking. In this way it is possible to monitor the blood pressure valuesof a person or animal.

Seventeenth Embodiment

Next, a seventeenth embodiment will be described.

This embodiment relates to a blood pressure measuring system.

FIG. 29 illustrates the blood pressure measuring system according to theseventeenth embodiment.

As illustrated in FIG. 29, the blood pressure sensor 210 and electronicequipment 510 is provided in the blood pressure measurement systemaccording to this embodiment. The blood pressure sensor 210 is fitted toa blood pressure measurement location of a subject. Here the bloodpressure measurement location is illustrated as the wrist. Theelectronic equipment 510 can include, for example, a television, amobile phone, a medical database, and a personal computer.

An internal processing unit 520 is provided in the blood pressure sensor210.

The processing unit 520 includes a first control unit 530 that controlsthe blood pressure sensor 210, a transmission unit 540 that transmitsinformation from the first control unit 530 externally, and a secondreception unit 550 that receives information from the outside andtransmits it to the first control unit 530. The information includesdata on blood pressure values, data on rates of change in electricalresistance, and data on electrical resistance values.

The electronic equipment 510 includes a reception unit 560, a secondcontrol unit 570, a calculation unit 580, a second transmission unit590, and a database (hereafter referred to as “DB 1”).

The reception unit 560 receives information transmitted from thetransmission unit 540 and transmits it to the second control unit 570.

The second control unit 570 transmits the information received from thereception unit 560 to the calculation unit 580, transmits it to thesecond transmission unit 590, or stores the information in the DB 1 asdata.

The calculation unit 580 carries out calculations on the informationtransmitted from the second control unit 570.

Exchange of information between the transmission unit 540 and thereception unit 560, and exchange of information between the secondtransmission unit 590 and the reception unit 550 can be by wirelesstransmission or by cable transmission.

Next, the operation of the blood pressure measurement system accordingto the seventeenth embodiment will be described.

FIG. 30 is a flowchart showing the operation of the blood pressuremeasurement system.

As illustrated in FIG. 30, in step S10, the first control unit 530instructs the blood pressure sensor 210 to measure the amount of changein electrical resistance at the blood pressure measurement location. Atthis time, the amount of change in electrical resistance in all themagneto-resistive effect devices provided in the blood pressure sensor210 is measured.

Next, in step S20, the first control unit 530 determines and selects themagneto-resistive effect device (MR device) on the blood pressuremeasurement location that is to be measured. Then, in step S30, theelectrical resistance of the selected MR device is measured. Next, instep S40, the transmission unit 540 transmits the measured electricalresistance value to the electronic equipment 510. The second controlunit 570 stores the received electrical resistance value data in thedatabase DB 1. Then, in step S50, the second control unit 570 transmitsthe electrical resistance value received by the reception unit 560 tothe calculation unit 580. The calculation unit 580 converts theelectrical resistance value to a blood pressure value.

Next, the effect of the blood pressure measurement system according tothe seventeenth embodiment will be described.

The blood pressure measurement system according to this embodimentincludes the magneto-resistive effect device which is suitable for highdensification, so it can be miniaturized. Therefore it can be used as anubiquitous health monitoring device that can be carried around whilewalking.

Eighteenth Embodiment

Next, a eighteenth embodiment will be described.

This embodiment relates to an air pressure meter.

In this embodiment, the strain sensor that incorporates themagneto-resistive effect device 110 according to the fifteenthembodiment is applied to an air pressure meter. The strain sensor inwhich the magneto-resistive effect device 110 according to the fifteenthembodiment is provided can distinguish between tensile strain andcompressive strain. Also, it can be miniaturized. For example, the airpressure meter according to this embodiment that includes this strainsensor is miniature, so it can be provided on the surface or back faceof a wing of an aircraft. Also, this air pressure meter can distinguishbetween negative pressure and positive pressure, so it can properlymeasure the changes in pressure produced on the surface or back face ofthe wing, so it is possible to know if the aircraft stalls or spins.

Nineteenth Embodiment

Next a nineteenth embodiment will be described.

This embodiment relates to a structural health monitoring sensor.

FIGS. 31 and 32 illustrate the structural health monitoring sensoraccording to the nineteenth embodiment.

As illustrated in FIG. 31, a plurality of structural health monitoringsensors 600 is provided on a surface of a bridge beam 610 of asuspension bridge.

Also, as illustrated in FIG. 32, a plurality of structural healthmonitoring sensors 600 is provided on the surface of an external wall620 of a building. Strain sensors according to the twelfth throughfifteenth embodiments are used in the structural health monitoringsensor 600 according to this embodiment. It can be easily checkedperiodically using the structural health monitoring sensors 600 whetherstrains have occurred in the bridge beam 610 or the external wall 620 ofthe building that are different from the initial state.

According to the embodiments as explained above, it is possible toprovide a magneto-resistive effect device, a magnetic head assembly, astrain sensor, a pressure sensor, a blood pressure sensor, and astructural health monitoring sensor that is suitable for highdensification.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modification as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A magneto-resistive effect device, comprising astacked body stacked on a substrate, the stacked body including a firstmagnetic layer that includes one or more metals selected from the groupconsisting of iron, cobalt, and nickel, a second magnetic layer stackedon the first magnetic layer, having a composition that is different fromthe first magnetic layer, and a spacer layer disposed between the firstmagnetic layer and the second magnetic layer; a pair of first electrodesthat feeds current to the stacked body; a strain introduction memberthat applies strain to the stacked body, that is provided near thestacked body, and by applying strain to the stacked body, biasesmagnetization directions of the first magnetic layer and the secondmagnetic layer in different directions; and a second electrode forapplying a voltage to the strain introduction member, wherein themagnetization directions of the first magnetic layer and the secondmagnetic layer are changed by the application of an external magneticfield, and the external magnetic field is detected by a change inresistance between the first electrodes due to the change in themagnetization directions.
 2. The device according to claim 1, whereinthe first magnetic layer has a positive magnetostriction coefficient,and the second magnetic layer has a negative magnetostrictioncoefficient.
 3. The device according to claim 1, wherein the strainintroduction member is disposed to the side of a film cross-section ofthe stacked body.
 4. The device according to claim 1, wherein the strainintroduction member includes one material selected from the groupconsisting of crystalline silicon oxide (SiO₂), zinc oxide (ZnO),KaC₄H₄O₆, lead zirconate titanate (PZT: Pb(Zr, Ti)O₃), lithium niobate(LiNbO₃), lithium tantalate (LiTaO₃), lithium borate (Li₂B₄O₇),langasite (La₃Ga₅SiO₁₄), aluminum nitride (AlN), polyvinylidenedifluoride (PVDF), gallium phosphate (GaPO₄), and tourmaline.
 5. Thedevice according to claim 1, wherein the strain introduction membereither directly contacts the stacked body, or contacts via an insulatingmaterial made from amorphous SiO₂ or amorphous Al₂O₃.
 6. The deviceaccording to claim 1, wherein an electrode is provided at about 45degrees or 135 degrees to the strain introduction member when viewedfrom the direction of application of the external magnetic field, inorder to apply a strain to the stacked body.
 7. The device according toclaim 1, wherein the first magnetic layer includes an oxide of one metalselected from the group consisting of iron, cobalt, and nickel.
 8. Thedevice according to claim 1, wherein the second magnetic layer includesone or more metals selected from the group consisting of nickel andsamarium iron (SmFe).
 9. The device according to claim 1, wherein thespacer layer includes an oxide or a nitride of one metal selected fromthe group consisting of aluminum, titanium, zinc, silicon, hafnium,tantalum, moylbdenum, tungsten, niobium, chromium, magnesium, andzirconium.
 10. A magnetic head gimbal assembly, comprising: amagneto-resistive effect device, wherein, the magneto-resistive effectdevice includes: a stacked body stacked on a substrate, the stacked bodyincluding a first magnetic layer that includes one or more metalsselected from the group consisting of iron, cobalt, and nickel, a secondmagnetic layer stacked on the first magnetic layer, having a compositionthat is different from the first magnetic layer, and a spacer layerdisposed between the first magnetic layer and the second magnetic layer;a pair of first electrodes that feeds current to the stacked body; astrain introduction member that applies strain to the stacked body, thatis provided near the stacked body, and by applying strain to the stackedbody, biases magnetization directions of the first magnetic layer andthe second magnetic layer in different directions; and a secondelectrode that applies a voltage to the strain introduction member,wherein the magnetization directions of the first magnetic layer and thesecond magnetic layer are changed by the application of an externalmagnetic field, and the external magnetic field is detected by a changein resistance between the first electrodes due to the change in themagnetization directions.
 11. A magnetic recording/reproduction device,comprising: a magnetic head gimbal assembly that includes amagneto-resistive effect device; a magnetic head that includes themagneto-resistive effect device, mounted on the magnetic head gimbalassembly; and a magnetic recording medium that reproduces informationusing the magnetic head, wherein the magneto-resistive effect deviceincludes a stacked body stacked on a substrate, the stacked bodyincluding: a first magnetic layer that includes one or more metalsselected from the group consisting of iron, cobalt, and nickel, a secondmagnetic layer stacked on the first magnetic layer, having a compositionthat is different from the first magnetic layer, and a spacer layerdisposed between the first magnetic layer and the second magnetic layer;a pair of first electrodes that feeds current to the stacked body; astrain introduction member that applies strain to the stacked body, thatis provided near the stacked body, and by applying strain to the stackedbody, biases magnetization directions of the first magnetic layer andthe second magnetic layer in different directions; and a secondelectrode that applies a voltage to the strain introduction member,wherein the magnetization directions of the first magnetic layer and thesecond magnetic layer are changed by the application of an externalmagnetic field, and the external magnetic field is detected by a changein resistance between the first electrodes due to the change in themagnetization directions.